III-nitride transistors are promising for high-speed and high-power applications, such as power switches, which may be used for motor drivers and power supplies, among other applications. Many of these applications require the transistor to operate in normally-off mode. Normally-off mode operation can be realized by a number of approaches, but typically at the penalty of higher on-resistance and lower output-current.
U.S. patent application Ser. No. 13/456,039, filed Apr. 25, 2012 describes a normally-off III-Nitride field-effect transistor and a method for making a normally-off FET.
What is needed is a normally-off FET, which has a minimal penalty in on-resistance. In particular what is desired is a high threshold voltage, preferably greater than one volt, a low on-resistance, preferably less than 20 ohm-mm for devices with more than 600V breakdown voltage, and an excellent uniformity in threshold voltage and on-resistance, with preferably less than 10% of standard deviation. The embodiments of the present disclosure answer these and other needs.